The goal of this proposed research is to understand the mechanisms underlying signal transduction in the olfactory system in Drosophila melanogaster utilizing a combination of molecular, genetic, behavioral and physiological approaches. Drosophila is a powerful model system to study olfaction because it allows the identification of genes responsible for each step of olfactory sensation and processing, and their assignment to specific physiologic and behavioral functions. The results of these studies will map the biochemical and cellular pathways necessary for olfactory signaling in Drosophila, and should direct future molecular genetic studies in analogous but more complex systems. 1) I will use enhancer trapping to isolate genes mediating olfaction from a collection of genes specifically expressed in the olfactory structures. I will initially use the cDNA sequences, patterns of expression and phenotypes of null mutations to suggest biochemical functions for these gene products. For selected genes, regulatory sequences will be isolated and used to express molecularly modified forms of these genes to define structure-function relationships. I have already used this strategy to isolate a gene, OBP-1 (odorant-binding protein-1), that encodes a novel member of the Drosophila odorant-binding protein family. Flies lacking OBP-1 have altered olfactory behavior. This is the first demonstration of a functional role for any member of this protein family in any system. 2) Signal transduction mechanisms mediating olfaction in Drosophila are not characterized. I have cloned a novel G protein alpha subunit, dGq- alpha-3, expressed in the olfactory system. Expression of dGq-alpha-3 in the dendrites of a subset of primary olfactory neurons suggests that it mediates a subset of olfactory responses. I will directly test this hypothesis by studying olfactory behavior in mutants specifically defective for dGq-alpha-3. In addition, several other classes of G protein alpha subunits are expressed in olfactory structures, and their contributions to olfactory signaling will be similarly determined. 3) Detecting olfactory phenotypes in Drosophila mutants has been hampered by the lack of an assay to simultaneously screen large numbers of odorant compounds. I have devised a novel behavioral assay to simultaneously screen large numbers of compounds for chemoattractive properties. I will continue to identify chemoattractive compounds for use in this assay.